1. Field
Embodiments relate to a method, system, and computer program product for consistent asynchronous replication of local backup.
2. Background
In certain storage system environments, a storage controller (or a storage controller complex) may comprise a plurality of storage servers that are coupled to each other. The storage controller allows host computing systems to perform input/output (I/O) operations with storage devices controlled by the storage controller, where the host computing systems may be referred to as hosts.
In many systems, data on one storage device may be copied to the same or another storage device so that access to data volumes may be provided from two different locations. The copying of a data set from a source volume to a target volume may be performed synchronously or asynchronously. In synchronous copy unless an acknowledgement is received that the data set has been written to the target volume, the host waits for the synchronous copy operation initiated by the host to complete, whereas in asynchronous copy the host does not have to wait for the asynchronous copy operation initiated by the host to complete.
Point in time copy allows creation of instantaneous, point in time snapshot copies of entire logical volumes or data sets. A point in time copy may involve physically copying all the data from source volumes to target volumes so that the target volume has a copy of the data as of a point in time. A point in time copy can also be made by logically making a copy of the data and then only copying data over when necessary. Certain storage subsystems are capable of performing “instant virtual copy” operations, also referred to as “fast replicate functions.” Instant virtual copy operations function by modifying metadata such as relationship tables or pointers to treat a source data object as both the original and copy. In response to a copy request from a host, the storage controller substantially immediately reports creation of the copy without having made any physical copy of the data. Only a “virtual” copy is created, and the absence of an additional physical copy is completely unknown to the host. A nocopy option for a point in time copy may perform a point in time copy without actually making a second copy of a dataset via some of the mechanisms described above or via other mechanisms.
When an application has one write that is dependent on the completion of another write, the application is said to have dependent writes. Using dependent writes, applications may manage the consistency of their data, so that a consistent state of the application data on storage devices is maintained, in the event of a failure in the host or the storage controller.
To maintain the consistency of data across multiple storage volumes at a remote backup location, certain storage controllers support the concept of a consistency group. Storage volumes in a copy relationship that are configured into a consistency group are maintained to ensure that a group of dependent updates made to the storage volumes at the primary location are made together as a unit on the storage volumes at the remote backup location to maintain data consistency.
Asynchronous remote copy is a mechanism that provides data replication over extended distances between two sites for business continuity, disaster recovery, and for other reasons. Asynchronous remote copy replicates the data asynchronously from a local site to a remote site.